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Brix refractometer accuracy evaluated

Measuring IgG levels in colostrum is an important means of both getting calves off to the healthiest possible start, and evaluating transition-cow nutrition. But it’s important to have practical tools to perform those routine measurements.

The Brix refractometer is a tool that measures the percentage of solids in a liquid by degrees Brix (°Bx), and is commonly used in the wine, sugar, fruit juice and honey industries. In the dairy setting, it is an inexpensive, durable, readily available tool that delivers quick results when used on-farm to measure colostrum IgG. An additional advantage is that its readings are not impacted by colostrum temperature, breed of the dam or season of the year.

With all of these advantages in its favor, it still is critical that the on-farm results delivered by the tool are consistent and accurate. A recent study at the University of New Hampshire sought to determine whether the results from theBrix refractometerwere accurate and reliable in measuring IgG levels in colostrum.

In the study, samples of first-milking maternal colostrum were collected from seven dairy farms in the Northeast U.S., and one farm in California. All samples were evaluated for total IgG content using the Brix refractometer, as well as by radial immunodiffusion (RID) and turbidimetric immunoassay (TIA). The Brix evaluation was performed on-farm, while the other two methods were conducted in laboratory settings.

Via exhaustive statistical evaluation of the three methods, the researchers concluded that the Brix refractometer does, indeed, consistently deliver accurate readings of IgG levels in colostrum. Its results were highly correlated with the two laboratory methods of evaluation. Based on their results, they recommend a reading of 21 percent on the Brix refractometer as the cut point for classifying colostrum as “high quality.”

Two additional interesting findings from the study include:

Colostrum quality decreases the longer the first milking is delayed after calving; and

The volume of colostrum produced did not increase by delaying milking after calving.

Both of these finding are consistent with previous studies, and suggest that cows should be milked out as quickly as possible after calving.